By using rhesus monkeys and human eyes which have a macula lutea we propose to investigate the dual nature of the optic nerve. We plan to study blood supply by injection techniques, fiber areas by image processing techniques, and composition and metabolism in monkeys only by radioisotope techniques. We plan to extend our study of the effect of intraocular pressure on optic nerve head circulation by measuring tissue oxygen content at the nerve head. We expect our work to contribute information applicable to glaucoma, multiple sclerosis and metal poisoning.